This invention relates to a spin molding process, a spin molding apparatus, a spin molding raw material, a spin molding process for a vehicle wheel, and a spin molding apparatus of a vehicle wheel.
As a process for manufacturing a vehicle wheel, there is a known process for applying a heat treatment after the spin molding is effected. In this manufacturing process, as the rim portion subjected to the spin molding is readily deformed by heating when a heat treatment is applied, it is necessary to take steps to prevent the air leakage of a tire. Therefore, when the spin molding is carried out, the rim portion 3, as shown in FIG. 23, is formed thicker than the final thickness (shown by the one dotted chain lines in the drawings). And after being subjected to the thermal treatment, such rim portion is cut into the final dimension.
However, the above-mentioned conventional manufacturing process for vehicle wheels has a first inconvenience in that as the thickness of the whole rim portion is formed greater than the final dimensions and the whole rim portion is cut after it is subjected to heat treatment, much time and labor are required for the cutting, and thus for the manufacturing of the vehicle wheel, and the yield of product from the material is lowered.
Also, when a vehicle wheel is spin molded in the prior art, it is performed so that raw material for a vehicle wheel is disposed on the periphery of a molding die (mandrel). The wheel raw material is drawn along the molding die by a rotary pressing device while rotating this raw material together with the molding die.
However, as the molding die (mandrel) is inherent in vehicle wheels, it is required to be exchanged with a separately prepared molding die (mandrel) when a vehicle wheel having different trim width is to be molded.
Therefore, there is a second inconvenience in that in order to spin mold a vehicle wheel, several kinds of molding dies (mandrels) must be prepared. As a consequence, the manufacturing cost of the molding dies (mandrels) is increased, and, in addition, it takes much time and labor for maintaining the molding dies (mandrels).
Also, in the prior art, when the spin molding is to be carried out, first the raw material is cast and such cast raw material is spin molded.
In this case, in the prior art, there were used, as a molding material, the so-called 4 C-material (for example, Cu: 0.006 wt. %, Mg: 0.33 wt. %, Fe: 0.12 wt. %, Mn: 0.006 wt. %, Ti: 0.115 wt. %, Sb: 0.112 wt. % and the remainder Al). By casting this molding member, a raw material is manufactured and this raw material is spin molded.
However, the conventional molding material, has a third inconvenience in that moldability is poor due to lack of expansion.
Also, in the prior art, for example, when a vehicle wheel W is to be spin molded, a disk portion D and a cylindrical rim portion 3 as shown in FIG. 24, are molded by forging or casting to obtain a wheel raw material or blank 1. And by drawing this raw material 1, which is engaged on the outer periphery of a rim molding mandrel 12, in the direction as shown by the arrow through a rotary pressing device 2, a rim portion 31 is formed (Japanese Patent Early Laid-Open Publication No. Sho 61-115640).
However, in such conventional spin molding process as mentioned above, when a cylindrical raw material blank to be molded (cylindrical rim raw material) 3 is placed on the molding mandrel (rim molding mandrel 12), this cylindrical raw material to be molded (cylindrical rim raw material) 3 is intimately contacted with a molding surface 126 of said molding mandrel (rim molding mandrel) 12.
Due to the foregoing arrangement, when such cylindrical raw material 3 as mentioned is drawn through the rotary pressing device 2, friction is generated between the cylindrical raw material 3 and the molding surface 126 of the mandrel 12. Therefore, it has a fourth inconvenience in that it takes much time and labor to draw the cylindrical raw material 3 along the projecting portion (rim flange molding portion) of the molding surface 126.
Also, in such conventional spin molding process as mentioned, as the cylindrical raw material to be molded (cylindrical rim raw material) 3 becomes gradually thinner as it goes toward the peripheral edge portion thereof, it has a fifth inconvenience in that the thickness of a rising portion 311 is difficult to increase, when the cylindrical raw material 3 is drawn by the rotary pressing device 2 along the projecting portion (rim flange molding portion) of the molding surface 126.
Furthermore, in such conventional spin molding process as mentioned above, as the thickness of the connecting portion between the cylindrical raw material to be molded (cylindrical rim raw material) 3 and a plate portion to be clamped (disk portion) D is great, there is a sixth inconvenience in that a decaying part is readily generated on the connecting portion 315 when the raw material 1 is cast and thus, the strength of a spin molded article is difficult to maintain.
Furthermore, in such conventional spin molding process as mentioned above, when the cylindrical raw material to be molded (cylindrical rim raw material) 3 is placed on the molding mandrel (rim molding mandrel) 12, this cylindrical raw material to be molded (cylindrical rim raw material) 3 is intimately contacted to the molding surface 126 of the molding mandrel (rim molding mandrel) 12.
Due to the foregoing, friction is generated between the cylindrical raw material 3 and the molding surface 126 of the mandrel 12 when the cylindrical raw material 3 is drawn by the rotary pressing device 2. Therefore, there is a seventh inconvenience in that it takes much time and labor to draw the cylindrical raw material 3 along the molding surface 126.
Also, in the prior art, when a vehicle wheel is spin molded, the wheel raw material is mounted on the molding mandrel and the wheel raw material is drawn by a pressing member along the molding surface of the mandrel while rotating the mandrel.
However, in such conventional spin molding process as mentioned above, the connecting portion between a spoke portion of a vehicle wheel and a rim portion is necessarily great in view of necessity of providing a drawing gradient to the mandrel. Therefore, there is an eighth inconvenience in that the weight of such a vehicle wheel easily becomes heavy.
Also, in the conventional spin molding, a cast raw material to be molded is placed on the mandrel and the raw material to be molded is drawn into a predetermined shape along the mandrel while rotating the raw material to be molded together with the mandrel and pressing the same with a pressing spatula.
However, as such spin molding process as mentioned above is a molding process which utilizes ductility of the cast raw material to be molded, there is a ninth inconvenience in that when such raw material to be molded is rapidly machined into a complicated shape, difficulty occurs in the raw material to be molded and cracks readily occur.
Also, in the spin molding apparatus, the raw material to be molded is drawn by the pressing member along the molding surface of the mandrel while clamping the raw material to be molded between the mandrel and the tail stock and rotating the mandrel. In this case, as for a raw material to be molded having a not-flat clamping surface (tail stock side) of the raw material to be molded, it is designed such that the contact surface of the tail stock is also intimately contacted with the clamping surface. Accordingly, when the raw material to be molded is clamped by the tail stock, correct positioning must be obtained by rotating the tail stock so that each contact surface of the tail stock is tightly contacted with the clamping surface of the raw material to be molded.
However, in the conventional spin molding process, as the tail stock and the mandrel can be independently rotated, when the raw material to be molded is to be clamped, a proper position (position where the contact surface of the tail stock can be tightly contacted with the clamping surface of the raw material to be molded) must be determined by rotating the tail stock after the raw material) to be molded is set to the material. Therefore, there is a tenth inconvenience in that when a spin molding is effected, it takes much time and labor for clamping the raw material to be molded.
Also, there is a case where it is required to show size, manufactured date, etc., on a spin molded article such as, for example, a vehicle wheel.
In this case, in the prior art, the above-mentioned items are shown by suitable means (for example, stamping) after the raw material to be molded is subjected to spin molding.
However, this way of showing the above-mentioned items on the vehicle wheel through a separate procedure after spin molding requires two steps of working processes. Therefore, there is an eleventh inconvenience in that the working efficiency of the spin molding is necessarily lowered.
The problem to be solved by the present invention is to eliminate the above-mentioned inconveniences inherent in the prior art.